Steering system service normally involves the adjusting or replacement of worn parts. Service is required when the worm shaft rotates back and forth without normal pitman arm shaft movement. This would indicate that there is play inside the gearbox. If excess clearance is NOT corrected after the adjustments, the steering gearbox must be replaced or rebuilt.
MANUAL GEARBOX ADJUSTMENT.- Since there are numerous steering gearbox configurations, we will discuss the most common type, recirculating ball and nut. There are two basic adjustments- worm bearing preload and over center clearance.
WORM BEARING PRELOAD- Assures that the worm shaft is held snugly inside the gearbox housing. If the worm shaft bearings are too loose, the worm shaft can move sideways and up and down during operation.
OVER CENTER CLEARANCE- Controls the amount of play between the pitman arm shaft gear (sector) and the teeth on the ball nut. It is the most critical adjustment affecting steering wheel play.
Set the worm bearing preload first and then the over center clearance.
The basic procedures for adjusting worm-bearing preload are as follows:
Disconnect the pitman arm from the pitman arm shaft. Loosen the pitman arm shaft overcenter adjusting locknut and screw out the adjusting screw a couple of turns. Then turn the steering wheel from side to side slowly.
Using a torque wrench or spring scale. measure the amount of force required to turn the steering wheel to the CENTER position. Note the reading on the torque wrench or the spring scale and compare it to the manufacturers specifications.
If readings are out of specifications. loosen the worm-bearing locknut. Then tighten the worm bearing adjustment nut to increase the preload. Loosen it to decrease preload and turning effort. With the preload set to specifications. tighten the locknut. Make sure the steering wheel turns freely from stop to stop.
If the steering wheel binds or feels rough, then the gearbox has damaged components and should be rebuilt or replaced.
The basic procedures for adjusting the over center clearance are as follows:
Find the CENTER position of the steering wheel. This is done by turning the steering wheel from full right to full left while counting the number of turns. Divide the number of turns by two to find the middle. This allows you to turn the steering wheel from full stop to the center.
Most gearboxes are designed to have more geartooth backlash (clearance) when turned to the right or left. A slight preload is produced in the center position to avoid steering wheel play during straight-ahead driving.
With the steering wheel centered, loosen the over center adjusting screw locknut. Turn the over center adjusting screw in until it bottoms lightly. This will remove the backlash.
Using the instructions in the service manual, measure the amount of force required to turn the steering wheel. Loosen or tighten the adjustment screw to meet the manufacturer's specifications. Tighten the locknut and recheck the gearbox action.
When adjustment fails to correct the problems, the steering gearbox needs to be overhauled or replaced. Overhauling a gearbox is done by disassembling, cleaning, inspecting, replacing worn components, and seals. After reassembling the gearbox. fill the housing with the correct type of lubricant. Most manual steering systems use SAE 90 gear oil. Make sure that you do NOT overfill the gearbox. Refer to the manufacturer's service manual for the particular gearbox you are working on since procedures, specifications, and type of lubricants vary.
RACK-AND-PINION SERVICE.- Rack-and- pinion steering systems have few parts that fail. When problems do develop, they are frequently in the tie-rod ends. When NOT properly lubricated, the rack and pinion will also wear, causing problems.
Depending upon the manufacturer, some rack-and-pinion steering systems need periodic lubrication. Others only need lubrication when the unit is being reassembled after being repaired.
Most rack-and-pinion systems have a rack guide adjustment screw. This screw is adjusted when there is excessive play in the steering. Basic procedure for adjusting rack-and-pinion steering system is as follows:
Loosen the locknut on the adjusting screw. Then
Tighten the locknut. Check for tight or loose steering and measure steering effort. Compare with the manufacturer's specifications. If not with specifications, an overhaul of the system will be required.
For instructions on the removal/ installation and overhaul of the rack-and-pinion system, refer to the manufacturer's service manual for the equipment you are repairing.